Generally, a semiconductor wafer, such as a silicon substrate, is subjected to various processes including a film-forming process, an etching process, and a diffusion process to fabricate a semiconductor integrated circuit.
Some of the processes inevitably deposit a reaction byproduct on the surface of, for example, a showerhead for introducing a process gas into a processing vessel. Such a reaction byproduct produces particles during a process. The showerhead or such is heated periodically or indeterminately to remove the reaction byproduct by sublimation without opening the processing vessel into the atmosphere.
This problem will be described with reference to FIG. 3 typically showing a conventional semiconductor wafer processing apparatus. Referring to FIG. 3, the semiconductor wafer processing apparatus has a processing vessel 4 provided in its lower part with an exhaust port 2 for vacuum evacuation. A susceptor 8 provided with a resistance heater 6 is placed in the processing vessel 4. A semiconductor wafer W is mounted on the susceptor 8.
A showerhead 12 provided with a plurality of gas holes 10 is attached to the top wall 14 of the processing vessel 4. A process gas, such as a film-forming gas, is introduced through the showerhead 12 into the processing vessel 4. A showerhead resistance heater 16 is embedded in the showerhead 12 to heat the showerhead when necessary. A cooling pipe 18 is embedded in the top wall 14 to cool the showerhead 12 indirectly when necessary. A pump 20 pumps a cooling liquid C, such as cooling water, to make the cooling liquid C flow through the cooling pipe 18.
After some wafers have been processed by the processing apparatus for a process, such as a film-forming process, a sublimable reaction byproduct deposits on the surface of the showerhead 12. Then, the showerhead heater 16 is energized to heat the showerhead 12 at a temperature at which the reaction byproduct sublimates, such as about 160° C., and the showerhead 12 is kept at this temperature for a predetermined time. The temperature of the showerhead 12 is decreased to perform the regular process, such as the film-forming process, immediately after the reaction byproduct has been removed by sublimation. The cooling liquid is passed through the cooling pipe 18 to cool the showerhead 12 indirectly to a temperature at which the film-forming process can be started, such as about 60° C.
The temperature of the showerhead 12 needs to be decreased rapidly to the predetermined process temperature and the film-forming process needs to be started immediately to increase the throughput of the film-forming process. Since the showerhead 12 of the conventional wafer processing apparatus is cooled indirectly by passing the cooling liquid through the cooling pipe 18 embedded in the top wall 14 supporting the showerhead 12, it takes a long time of, for example, 20 minutes or longer, to cool the showerhead 12. Thus, the throughput of the film-forming process is reduced.
It may be possible to cool the showerhead 12 directly by embedding the cooling pipe 18 in the showerhead 12 instead of in the top wall 14. However, if the cooling pipe 18 is embedded in the showerhead 12, the cooling liquid remaining in the cooling pipe 18 will evaporate due to rapid heating and pressure in the cooling pipe 18 will sharply increase. Consequently, the sharply increased pressure acts directly to a cooling system including pipes and the pump 20 connected to the cooling pipe 18 and it is possible that the cooling system is damaged.
Thus, there has been demand for a processing apparatus provided with a cooling mechanism capable of rapidly decreasing the temperature of a member to be cooled, such as a showerhead.